During the formation of semiconductor devices, such as dynamic random access memories (DRAMs), insulating layers are used to electrically separate conductive layers. It is often required that the conductive layers be interconnected through openings in the insulating layer. Such openings are commonly referred to as contact holes (i.e., an opening extending through an insulating layer to an active device area) or vias (i.e., an opening extending through an insulating layer between two conductive layers).
The profile of an opening is of particular importance such that it exhibits specific characteristics when the contact hole or via is provided or filled with a conductive material. As minimum feature dimensions of devices decrease, the aspect ratio (the ratio of depth to width) of the openings needs to increase. As the aspect ratio increases, however, a phenomenon termed “twisting” can occur. Twisting occurs when the etch front of the opening starts deviating from what is perpendicular to the semiconductor substrate surface, for example, openings in the shape of a corkscrew are possible. The twisting phenomenon with respect to high aspect ratio (HAR) openings is problematic in that twisting reduces the efficiency of a contact by increasing the distance between active device areas and by increasing the difficulty of filling a contact with a conductive material. As such, a suitable solution to the twisting phenomenon in HAR etch processes is desired.